Re: [PATCH] mfd: macsmc: Fix key count endianness annotation

["Joshua Peisach" <jpeisach@ubuntu.com>]

On Sun Jul 19, 2026 at 11:15 AM EDT, Sven Peter wrote:
>
>
> On 7/19/26 17:02, Joshua Peisach wrote:
>> On Sun Jul 19, 2026 at 9:00 AM EDT, Sven Peter wrote:
>>> SMC firmware returns the value of the #KEY key in big-endian unlike most
>>> other keys. Reading it through apple_smc_read_u32() into a plain u32
>>> and then converting with be32_to_cpu() makes sparse complain:
>>>
>>>   drivers/mfd/macsmc.c:462:26: sparse: cast to restricted __be32
>>>
>>> Read the raw value into a __be32 using apple_smc_read() instead.
>>>
>>> Fixes: e038d985c982 ("mfd: Add Apple Silicon System Management 
>>> Controller")
>>> Reported-by: kernel test robot <lkp@intel.com>
>>> Closes: 
>>> https://lore.kernel.org/oe-kbuild-all/202607181046.OANjIoqR-lkp@intel.com/
>>> Signed-off-by: Sven Peter <sven@kernel.org>
>>> ---
>>>  drivers/mfd/macsmc.c | 8 +++++---
>>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/mfd/macsmc.c b/drivers/mfd/macsmc.c
>>> index 358feec2d088..514cba7dc897 100644
>>> --- a/drivers/mfd/macsmc.c
>>> +++ b/drivers/mfd/macsmc.c
>>> @@ -410,7 +410,7 @@ static int apple_smc_probe(struct platform_device 
>>> *pdev)
>>>  {
>>>      struct device *dev = &pdev->dev;
>>>      struct apple_smc *smc;
>>> -    u32 count;
>>> +    __be32 count;
>>>      int ret;
>>>
>>>      smc = devm_kzalloc(dev, sizeof(*smc), GFP_KERNEL);
>>> @@ -461,8 +461,10 @@ static int apple_smc_probe(struct 
>>> platform_device *pdev)
>>>      dev_set_drvdata(&pdev->dev, smc);
>>>      BLOCKING_INIT_NOTIFIER_HEAD(&smc->event_handlers);
>>>
>>> -    ret = apple_smc_read_u32(smc, SMC_KEY(#KEY), &count);
>>> -    if (ret)
>>> +    ret = apple_smc_read(smc, SMC_KEY(#KEY), &count, sizeof(count));
>>> +    if (ret >= 0 && ret != sizeof(count))
>>> +        ret = -EINVAL;
>>> +    if (ret < 0)
>>>          return dev_err_probe(smc->dev, ret, "Failed to get key count");
>>>      smc->key_count = be32_to_cpu(count);
>>
>> This makes sense, it just feels weird reading because u32 is.. not a
>> be32 (that gets passed into be32_to_cpu).
>
> count is __be32 now (the SMC firmware returns that value as big-endian 
> because Apple likes to think different) and we read that using 
> apple_smc_read now which just reads raw bytes. be32_to_cpu then converts 
> that to a u32, i.e. the type of smc->key_count. There's no functional 
> change here. What's weird about that?
>
>
> Sven

Pfft, brain fart. I thought you were going other way around.

Reviewed-by: Joshua Peisach <jpeisach@ubuntu.com>